This invention relates to a workpiece heating chamber, and, more particularly, to a workpiece heating chamber having a controlled internal atmosphere.
Welding of certain metal articles, for example gas turbine engine components made of a high temperature Ni base superalloy, is conducted at elevated temperatures within a chamber in which the atmosphere is controlled to be non-oxidizing. Typically argon gas is used for that purpose. An operator such as a welder applies a weld metal, for example in the form of a metal rod, to a portion of the article, frequently in the repair but also in the original manufacture of the article. Associated with the chamber is a heat source such as a high temperature heat lamp capable of heating at least a portion of the workpiece and the metal rod used for welding to an appropriate temperature range.
Several problems exist with such apparatus currently in use. One is that contamination of the atmosphere within the chamber by oxygen has occurred as a result of ambient air seeping into the chamber. One area of contamination entry has been observed to be at an operator access port through which the operator works; another such area is at a joint between the heat source and a wall of the chamber. The presence of an oxidizing material such as oxygen from air can reduce weld quality, resulting in weld cracks. In addition, the presence of oxygen in such a chamber can result in poor flowablity of the weld material as well as in detrimental inclusions in the weld itself. Another problem with known apparatus relates to the accurate and reproducible alignment of the heat source, which must be replaced from time to time, with a position within the chamber at which the workpiece is held for welding. As a result of problems such as these, known chambers were unable to maintain a consistent non-oxidizing temperature condition during welding.